1. Field of the Invention
The present invention relates generally to hip arthroplasty and pertains, more specifically, to apparatus and method for conducting interoperative trailing to determine an appropriate neck length and head offset in the femoral component of a prosthetic hip joint.
2. Description of Related Art
Total hip arthroplasty requires the preparation of an implant site for the reception of a femoral component and an acetabular component of a prosthetic hip joint to be implanted at the implant site. Proper hip mechanics are achieved through the selection of an appropriate neck length and head offset in the femoral component of the prosthetic hip implant. That is, the distance between the stem of the femoral component and the femoral head of the component, provided by the length of the neck along a predetermined direction of the neck, and the lateral offset between the stem of the femoral component and the femoral head, establishes the requisite neck length and head offset which, in turn, provides the desired range of motion, leg length, and tension in the soft tissue at the implant site. Accordingly, of utmost importance is the ability to determine the appropriate neck length and head offset with precision, and to do so with ease and assurance.
A determination of the appropriate length required for the neck of a femoral component and the appropriate head offset is conducted once the size of each of the femoral component and the acetubular component is selected, and the implant site is prepared for the reception of each selected component. A preliminary assessment can be made utilizing radiographic analysis; however, a final determination usually is accomplished during the course of the implant procedure itself, that is, interoperatively.
In a current trailing procedure, serial trial prostheses are used to determine the appropriate neck length and head offset during the conduct of total hip arthroplasty. Thus, the hip joint is dislocated, a provisional trial prosthesis is put into place, the hip joint is reduced, and the leg of the patient is moved by a surgeon through a range of motion to determine hip mechanics, by hand. The trailing procedure requires that the trial prosthesis be removed and replaced with another in a series of trial prostheses in order to evaluate the effect of different neck lengths and head offsets on hip mechanics. To achieve correct hip mechanics, a surgeon may need to perform several iterations, each requiring replacement of one trial prosthesis with another in the series, reduction of the hip joint, movement through a range of motion, and then dislocation of the joint again in order to change trials. The procedure can be quite time-consuming and even physically challenging, especially with larger patients. Moreover, the procedure is not suited to the conduct of more recently developed minimally invasive total hip arthroplasty where access to the hip joint is more limited.